Preheat your oven to 350°F (180°C). Grease an 8-inch (20 cm) round cake pan or line it with parchment paper.
Whip the eggs and sugar together in a large bowl until they’re light and fluffy. This takes about 5–7 minutes with an electric mixer. You want them pale, foamy, and airy!
Sift the flour and baking powder over the egg mixture and gently fold it in using a spatula. Be gentle here, we don’t want to knock out all that lovely air.
Add the vanilla sugar and melted butter, folding again just until combined.
Pour the batter into your cake pan and bake for 20–25 minutes, or until it’s golden brown and a toothpick comes out clean.
Cool completely on a rack, then cut into cubes. Try not to snack on too many pieces while you’re at it. (It’s tough, I know!)